<template>
    <ul class="list">
        <li class="item" 
        v-for="item of letters" 
        :key="item"
        :ref="item"
        @touchstart="handleTouchStart"
        @touchmove="handleTouchMove"
        @touchend="handleTouchEnd"
        @click="handleLetterClick">{{item}}</li>
    </ul>
</template>
<script>
export default {
    name:'CityAlphabet',
    props:{
        cities:Object
    },
    data(){
        return {
            touchStatus:false,
            startY:0,
            timer:null
        }
    },
    updated(){
        this.startY = this.$refs['A'][0].offsetTop;
    },
    computed:{
        letters(){
            const letters =[]
            for(let i in this.cities){
                letters.push(i)
            }
            return letters;
        }
    },
    methods:{
        handleLetterClick(e){
            // console.log(e.target.innerText);
            this.$emit('change',e.target.innerText);
        },
        handleTouchStart(){
            this.touchstatus = true 
        },
        handleTouchMove(e){
            // 节流
            if(this.timer){
                clearTimeout(this.timer)
            }
            this.timer = setTimeout(()=>{
                    if(this.touchStatus){
                    const touchY = e.touches[0].clientY - 79
                    const index = Math.floor((touchY-this.startY)/20);
                    // console.log(touchY)
                    if(index >= 0 && index< this.letters.length){
                        this.$emit('change',this.letters[index])
                    }
                }
            },16)
           
        },
        handleTouchEnd(){
            this.touchstatus = false 
        }
    }
}
</script>
<style lang="stylus" scoped>
@import "~styles/varibales.styl"; 
.list
    display:flex
    flex-direction :column
    justify-content :center
    position:absolute
    top:1.58rem
    right:0
    bottom:0
    wifth:.4rem
    .item
        text-align :center
        line-height :.44rem
        color :$bgColor
</style>